The present invention relates to electro-mechanical systems for inspecting the insides of buried pipes and other conduits for defects and obstructions, and more particularly, to a video pipe inspection system with improved distance measuring capabilities.
There are many situations where it is desirable to internally inspect long lengths of pipe which are already in place, either underground, in a building, or underwater. For example, sewer and drain pipes frequently need to be internally inspected to diagnose existing problems or to determine if there are any breaks causing leakage or obstructions impairing the free flow of waste. It is also important to internally inspect steam pipes, heat exchanger pipes, water pipes, gas pipes, electrical conduits and fiber optic conduits for similar reasons. Frequently, pipes which are to be internally inspected have an internal diameter of six inches or less. It is sometimes necessary to inspect several hundred feet of pipe.
Over the years, video pipe inspection systems have been developed which typically include a camera which is forced down the pipe so that its interior can be viewed on a video display. It is common to record the inspection on a video recorder (VCR). Conventional video pipe inspection systems include a push cable which provides an electro-mechanical connection between a rugged head enclosing and protecting the video camera and a rotatable push reel which is used to pay out cable and force the head down the pipe. The push cable must be specially constructed in order to be flexible enough to make tight turns yet rigid enough to be pushed hundreds of feet down small diameter pipe. The push cable must also incorporate electrically conductive or fiber optic cable having the proper impedance for conveying the NTSC or other video signal to the video display unit and additional power and ground conductors. Examples of video push cables are disclosed in U.S. Pat. No. 5,457,288 granted Oct. 10, 1995 to Mark S. Olsson and U.S. Pat. No. 5,808,239 granted Sep. 15, 1998 to Mark S. Olsson.
In a video pipe inspection system it is highly desirable for the user to have accurate information concerning the location of the camera head in the pipe. This is important in establishing the location of the defect or obstruction that must be repaired, e.g. by excavation. The amount of push cable that has been forced down the pipe can be measured and the approximate location of the camera head in the pipe can be determined from this measurement. An electromagnetic/inductive transmitter can also be mounted adjacent the camera head whose output signal can be detected above ground as an additional or alternate means of locating the camera head.
In commercial video pipe inspection systems the amount of push cable that has been payed out from the push reel and forced down the pipe and the amount of push cable that has been withdrawn have been measured in two basic ways. A first approach uses a pair of pinch rollers adjacent the push reel and between which the push cable is fed. The rollers are driven by the movement of the push cable and conventional mechanical or electrical mechanisms provide a visual read out of the length of push cable that has been payed out or pulled in. This approach is cumbersome and subject to problems because the pinch rollers often get fouled by dirt and other debris drawn from the pipe. The pinch rollers can slip or lock up and provide inaccurate distance measurements.
A second approach that has been used commercially to measure the amount of push cable forced down a pipe requires an optical encoder or other device which is mechanically driven by the push reel. The number of rotations of the push reel, along with the direction of rotation of the push reel, provide a measurement of the length of push cable that has been payed out or pulled in from the pipe. Signals from the optical encoder are sent to a processing circuit, usually associated with the video display, where they are processed so that alphanumeric distance information can be simultaneously displayed as an overlay to the real time video image of the interior of the pipe. The optical encoder can fail as a result of the harsh environment in which video pipe inspection systems are frequently used. A video pipe inspection system that has an optical encoder or some other electrical motion sensing device mechanically driven by the push reel requires a special electronic circuit. The controls and user programming of the special electronic circuit are often complex and not user friendly. The output of a video pipe inspection system with a mechanically driven push reel motion sensor cannot typically be plugged into any household TV or VCR. Thus the special distance signal processing unit represents added expense to the end user as well as more equipment to haul between job sites.
It is therefore the primary object of the present invention to provide a video pipe inspection system with improved distance measuring capabilities.
In accordance with the present invention a video pipe inspection system includes a video camera head with an optical sensor connected to a circuit for generating a video image signal representing real time images of scenes in view of the optical sensor. The system further includes a push reel that is rotatably mounted on a support frame. An elongate push cable is normally stored in continuous turns in the push reel. The push cable has a distal end operatively connected to the video camera head and a proximal end operatively connected to a central hub of the push reel. The push cable includes at least one conductor for conveying the video image signal from the camera head. The push cable has a predetermined resiliency and flexibility to permit the push cable to be unwound from the push reel in order to force the camera head a substantial distance down a length of pipe. A distance sensing module is mounted to the frame and includes two non-contact sensor pairs for detecting an amount and a direction of relative motion of the push reel and for providing a video overlay signal representing a length of the push cable that has been pushed into the pipe. An electrical connection is provided between the proximal end of the push cable and the distance sensing module so that the video overlay signal can be joined with video image signal from the camera head to provide an output video signal. The output video signal is transmitted via cable, RF or any other suitable manner to a video display unit that shows real time images of the interior of the pipe along with a visual indication of the length of push cable that has been forced down the pipe.
The present invention also provides a method of internally inspecting a pipe. The first step of the method involves providing a video camera head including an optical sensor and means for generating a video image signal representing real time images of scenes in view of the optical sensor. The next step of the method calls for connecting the video camera head to a distal end of an elongate push cable having a predetermined resiliency and flexibility to permit the camera head to be forced down a substantial distance of a length of pipe. The next steps of the method require storing the push cable in a plurality of turns in a push reel and mounting the push reel for rotation on a support frame. The next step of the method involves detecting an amount and direction of rotation of the push reel via a distance sensing module mounted on the frame and generating a video overlay signal representing a length of the push cable that has been payed out of and/or reeled into the push reel and forced down the pipe. The next step of the method requires communicating the video image signal from a proximal end of the push cable to the distance sensing module and joining the video image signal and the video overlay signal to provide an output video signal. The final step of the method involves communicating the output video signal to a video display unit and displaying real time images of the inside of the pipe while simultaneously displaying a position of the video camera head inside the pipe representative of the length of the push cable that has been payed out of and/or reeled into the push reel.